Colored anodized aluminum article and alloys therefor



Oct. 15, 1963 M. c. FETZER ETAL 3,107,159

COLORED ANODIZED ALUMINUM ARTICLE AND ALLOYS THEREFOR Filed Feb. 4. 1957 INVENTORS MAURICE O. FETZER PHILIP R. SPERRY JAMES F. MURPHY ATTORNEY United States Patent 3,107,159 COLQRED ANGDIZED ALUMINUM ARTICLE AND ALLGYS THEREFGR Maurice C. Fetzer, Spokane, and Philip R. Sperry, Opportunity, Wash, and James F. Murphy, Scotia, N.Y., as-

signers to Kaiser Aluminum & Qhemieal Corporation,

Oakland, Calif., a corporation of Deiaware Filed Feb. 4, 1957, Ser. No. 636,911 35 Claims. (G. 29-195) This invention relates to composite articles having a particular aluminum metal base portion coated with an artificially produced oxide film, the process for producing such composite articles and the aluminum base alloy. More particularly, this invention relates to aluminum alloys particularly adapted for the production of colored surfaces thereon by coating with an artificially produced oxide film, and to the resulting composite article.

This application is a continuation-in-part of application Serial No. 577,999, filed April 13, 1956, now abandoned.

For many purposes aluminum surfaces are protected by an oxide film produced on the surface by exposure as an anode in an acid electrolyte capable of yielding oxygen on electrolysis, such as an aqueous solution of Sulfuric acid or oxalic acid. The operation of forming such films is commonly termed anodizing and the aluminum surface thus protected is commonly termed anodized. It has long been desired to color such oxide coated aluminum surfaces. In the past, however, such colored surfaces have been produced by first anodizing the aluminum metal base and thereafter dyeing the anodic coating with organic dyes. Another means for producing colored aluminum surfaces is by the ferric oxalate hydrolysis process which deposits ferric oxide or hydrate in the pores of the anodic coating. This process requires first anodizing the aluminum metal base followed by immersion of the anodized aluminum in a solution of ferric animonium oxalate at controlled concentration, temperature and pH. A third means for producing colored aluminum surfaces involves the double precipitation of an insoluble colored inorganic compound. Such processes possess certain inherent disadvantages particularly with regard to the number of process steps required to produce a colored surface. For example such prior art processes require the anodized metal to be subjected to at least one additional processing step in order to color the anodic coating. In addition where the color is produced by impregnating the anodic coating with a dye, the colors tend to fade rapidly when exposed to ultra violet light.

Accordingly, it is a primary purpose and object of this invention to provide an aluminum base article having a colored anodic film adhering thereto characterized by pleasing appearance and superior light fastness.

It is a further object of this invention to provide a colored composite article featuring a particular aluminum metal base portion wherein said colored article may be produced by simply coating the aluminum metal base portion With an artificially produced oxide film without subjecting the oxide coated surface to a separate coloring treatment.

It is a' further object of this invention to provide a colored aluminum base composite article characterized by superior light fastness and desirable appearance including absence of undesirable streaks and visible surface "ice grains and featuring an aluminum metal base portion particularly adapted to the production of such a colored article by simply coating the aluminum metal base portion with an artificially produced oxide film without subecting the oxide coated surface to a separate coloring treatment.

It is a further object of this invention to provide a gold or bronze colored aluminum base-anodized composite article characterized by superior light fastness, strength and desirable appearance and featuring an aluminum metal base portion particularly adapted for the production of such a colored article by anodizing without the necessity of subjecting the anodized surface to a separate color treatment.

It is a further object of this invention to provide aluminum alloys particularly adapted for the production of colored articles characterized by superior light fastness and desirable appearance by simply coating said alloys With an artificially produced oxide film without the necessity of subjecting the coated alloy to a separate color treatment.

It is a 'funther object of this invention to provide a wrought aluminum base alloy material having an adherent gold colored anodic film thereon characterized by pleasing appearance and superior light fastness.

It is a further object of this invention to provide a Wrought aluminum base alloy material having an adherent bronze colored anodic film thereon characterized by pleasing appearance and superior light fastness.

These and other objects and advantages of the invention will be apparent from the following detailed description thereof.

It has been discovered according to the invention that certain chromium containing aluminum base alloys, in which the amount of chromium and the presence and amounts of certain elements other than aluminum and chromium are precisely controlled, may be coated with artificially produced oxide films to obtain composite articles having a gold colored surface of any predetermined shade characterized by pleasing appearance and superior light fastness without the necessity of subjecting the coated articles to a separate color treatment. Certain impurity elements which are inherent in the aluminum pig material and the certain other positively added elements, hereinafter specified, must be precisely controlled within strict requirements in order to obtain the desired shade of gold and to maintain the reproducibility of the desired shade. The positively added elements, other than chromium and aluminum, may be added to the alloys to increase the strength, to vary the color of the anodic coating, to refine the grain structure, etc. By properly controlling the impurity elements and/ or the amounts of the positively added elements, as Well as the chromium content, shades of goldv color varying from light gold to a deep gold can be obtained and reproduced. Also, by the proper control of element addition, a bronze color can be obtained and reproduced.

In general, the aluminum base alloys of the invention contain from about 0.2 to about 0.5% chromium by Weight, the preferred range of chromium being from about 0.2 to 0.4% by Weight. It has been found that when an alloy With a chromium content Within these however, with increased chromium content the fabrication of the alloy tends to become more .difficult. It has been found that a minimum of about 0.2% chromium is necessary to obtain an appreciable color effect on the anodized article.

With chromium contents in the alloys above about 0.4%, primary crystals (CI'Alq) tend to form during cooling of the molten metal and as the chromium content increases the amount of primary crystals increases. These crystals, depending upon size, amount, and positional relationship, tend to have an adverse effect on the appearance of the final anodized article. During the anodizing procedure, there is a tendency for the electrolytic solution to attack the peripheral boundaries of the primary crystals thereby causing the crystals to be removed leaving pits which detract from the uniformity and appearance of the metal surface underlying the anodic coating. Also, on working the metal ingot into a Wrought shape, as by rolling or extrusion, the primary crystals present on the surfaceof the ingot tend to fracture into a plurality of particles generally along lines longitudinal to the working direction. Upon anodizing such shapes, the selective attack of the electrolyte tends to manifest itself in the form of bands or streaks of color of a shade slightly different from the color of the balance of the surface. However, it has been found that by selection of proper casting conditions and close control there-' of the adverse effect of primary crystals up to a certain extent can be overcome or reduced to a point where an acceptable color uniformity can be produced for certain ultimate applications. Although the preferred range of chromium content in alloys of this invention is from about 0.2 to 0.4% by weight, wherein no primary crystal formation is present, chromium contents slightly in excess of 0.4% by weight and up to about 0.5% by weight have been used under certain conditions, as mentioned hereinabove, and were productive of an acceptable gold color composite article. 7

Where the colored composite article of this invention is to be used in applications requiring a strength greater than that found in the above-described alloys, such alloys may be clad onto a base layer of a metal having higher strength, such as a higher strength aluminum alloy according to conventional clading practices. The high strength metal may be clad on one or both sides with the aluminum alloys of this invention. The clad surface may nates a layer of colored anodic oxide film.

'Where the alloys of the instant invention are to be ultimately used in unclad form, this invention contemplates the addition of the element magnesium to the aluminum alloys for purposes of improving the strength of the alloys. Amounts of magnesium up to about 1.2% by'weight are found to add appreciably to the strength .of the alloys with only a very slight diminution in the Y color intensity of the anodized coating and lustre of the composite article. Generally it is preferred that the magnesium be present in an amount ranging from 0.4 to 0.6% by weight.

It has also been found according to the invention that the addition of the element manganese, in amounts up to' about 0.6% by weight, to the aluminum base alloys described above imparts a different color to the anodized article than that produced by the presence of chromium alone. Generally it is preferred that the manganese be present in an amountranging from 0.2 to 0.6% by weight. In general, with the above chromium containing alloys a gold color is obtained upon anodizing whereas with the aluminum base alloys containing both chromium and manganese, with or without magnesium, the color obtained upon anodizing is bronze and this color can be controlled to vary from light to dark bronze by the proper control of the addition constituents chromium and manganese.

This invention also contemplates the additions of titanium in amounts from about 0.02% to about 0.10% by weight which are beneficial to the alloys of this invention, particularly to the aluminum-magnesium-chromium ternary alloys discussed above. The alloys of this invention, which are of relatively high purity aluminum, are characterized by a relatively coarse grain structure in the as-cast state. Titanium added to the alloys in the amounts discussed above will result in a relatively fine grain structure in the as-cast state and which fine grain structure will be productive of a more uniform surface appearance. No adverse effect on the color of the anodized coating has been found to fiow from the addition of the element titanium. Other grain refining elements may be added to thealloys of this invention. It is to be distinctly understood that titanium is but one example of the suitable grain refining element and it is within the scope of this invention to employ other element additions which will perform the same function in the alloys of this invention.

it is essential in attaining the principal objects of this con present in the alloys not be in excess of 0.35% by weight and preferably not over 0.20% by weight. It has also been found that in the magnesium containing alloys of this invention, as the magnesium content increases the total iron plus silicon content should be lowered from the maximum of 0.35% in order to maintain the desired lustre or brightness of the colored anodic film. For example, where magnesium is present in amounts on the order of 1% by weight the total iron plus silicon should not exceed about 0.03% byweight for optimum results. Other residual or impurity elements, e.g. copper and zinc, may be present in the alloys of this invention in normal impurity amounts without adversely {afiecting the beneficial results obtained by the combinations of chromium and other alloying constitutents hereinbefore discussed with the aluminum metal.

The anodizing of the alloys of this invention may be carried out in either sulfuric or oxalic acid electrolytes or a mixture of both. of these acid electrolytes it is preferred that oxalic acid be used in that it has been found that with the same anodizing time the use of oxalic acid electrolyte is productive of the same gold color as is produced by using a sulfuric acid electrolyte wherein the alloy contains a higher chromium content; Alternatively with the same chromium content oxalic acid will produce two to three times the color intensity in a given anodizing time as is produced by sulfuric acid in the same anodizing time. As a compromise a mixed anodizing bath of oxalic and sulfuric acids may be employed. Such a bath gives anodizing voltage characteristics similar to a sulfuric acid anodizing bath and has color intensity development characteristics almost as good as a bath employing oxalic acid alone.

Depending upon the lustre or brightness of the colored anodized aluminum base alloy desired, that is, the degree, of specular reflectance, the alloys of this invention may be subjected to various pretre-atments prior to anodizing. For example, where high lustre or brightness is desired, the base metal may be subjected to conventional polishing or brightening treatments, e.g. mechanical, chemical, or electrochemical. Where it is desired that the ultimate article have a matte or satin appearance, the base metal can be subjected to a suitable etching treatment. Examples of satisfactory pretreatment and anodizing procedures utilizing oxalic and sulfuric acid are set forth below, it being understood that the conventional water rinsing operations after various steps are not recited.

Oxalic acid anodizing:

(1) Clean metal in an inhibited alkaline cleaner.

(2) (a) Where high lustre or brightness of ultimate colored composite is desired, treat metal according to a suitable bright dip process such as that described in U.S. P-at. 2,719,781. (b) Where matte appearance is desired in ultimate composite, subject material to caustic etch treatment in solution of 5% sodium hydroxide plus 2% sodium fluoride maintained at 160 F.-5 minute immersion period.

(3) Rinse in 50% by volume nitric acid solution.

(4) Anodize for 15 to 90 minutes in 2 to oxalic acid solution maintained at a temperature of from approximately 75 to 100 F. Voltage may be 45 to 55 volts and current density may be 10 to 30 amperes per square foot.

(5 Seal the porous oxide film by immersion in hot water at 180 to 200 F. for 10 minutes.

Slufuric acid anodizing:

(1) Clean metal in an inhibited alkaline cleaner.

(2) (a) Where high lustre or brightness of ultimate suitable bright dip process such as that described in colored composite desired, treat metal according to a U.S. Pat. 2,719,781. (12) Where matte appearance is desired in ultimate composite, subject material to caustic etch treatment in solution of 5% sodium hydroxide plus 2% sodium fluoride maintained at 160 F.-5 minute immersion period.

(3) Rinse in 50% by volume nitric acid solution.

(4) Anodize for 30 to 90 minutes in a 10 to 20% sulfuric acid bath maintained at a temperature of 60 to 85 F. Voltage may be 7 to 24 volts and current density may be from 5 to 20 amperes per square foot.

(5) Seal the porous oxide film by immersion in hot water maintained at a temperature of from 180 to 200 F. for a period of 10 minutes.

Mixed oxalic and sulfuric acid anodizing:

(1) Clean metal in an inhibited alkaline cleaner.

(2) (a) Where high lustre or brightness of ultimate colored composite desired, treat metal according to a suitable bright dip process such as that described in U.S. Pat. 2,719,781. (12) Where matte appearance is desired in ultimate composite, subject material to caustic etch treatment in solution of 5% sodium hydroxide plus 2% sodium fluoride maintained at 160 F.-5 minute immersion period.

(3) Rinse in 50% by volume nitric acid solution.

(4) Anodize for to 90 minutes in a solution comprising 2 to 10% oxalic acid and 5 to 15% sulfuric acid maintained at a temperature of from approximately 75 to 100 F. Voltage may be 8 to 28 volts and current density may be 10 to 30 amperes per square foot.

In order to establish the superior light fastness of the colored composite articles produced by anodizing the chromium containing alloys of this invenion over those produced by the conventional dyeing and pigment preoipitation methods of the prior art, laboratory tests described hereinbelow have been conducted. The test results which are herein disclosed are not intended to limit the invention but rather to clearly demonstrate the superiority thereof.

Anodized samples of an aluminum-chromium binary 5 alloy of the invention containing 0.39% chromium by Weight were exposed in a high intensity ultraviolet ilglt cabinet. The complete chemical composition of the aluminum alloy was 0.39% chronium, 0.07% silicon, 0.14% iron, 0.03% titanium, balance aluminum. After these anodized samples had been exposed to high intensity ultraviolet light for a period of 1000 hours, it was found that there was only a 10% loss of color intensity.

For comparative purposes, 10 samples of 5005 aluminum alloy were anodized. The chemical composition of the 5005 aluminum alloy was 0.20% silicon, 0.55% iron, 0.08% copper, 0.02% manganese, 0.69% magnesium, 0.5% zinc, 0.02% titanium, balance aluminum. Five of the samples were dyed for 10 minutes in Bates No. 6 yellow dye, 1 gram per liter, and 5 were gold colored by the ferric oxalate hydrolysis process which deposits yellow ferric oxide or hydrate pigment in the pores of the anodic coating. The samples of the organic dye had a 70% loss of color intensity after 376 hours exposure in the ultraviolet light test cabinet. Ferric oxide pigment had a 40% loss of color intensity after 1000 hours exposure in the ultraviolet light test cabinet.

These comparative results are more clearly shown in the table below:

In each of the above tests the aluminum base metal was anodized by treatment in a sulfuric acid anodizing electrolyte starting with the following pre-treatment:

( 1) Cleaned in an inhibited alkaline cleaner to a Water break free surface.

(2) Rinsed in cold water.

(3) Bright dipped according to the teaching of U.S. Patent 2,719,781 using a temperateure of 200 F.

(4) Rinsed in by volume nitric acid.

(5) Rinsed in cold water.

The above pro-treatment ensured a uniformly clean surface for anodizing. After the above pre-treatment, the samples were direct current anodized in 15 sulfuric acid solution with a current density of 12 amperes per square foot. The temperature of the anodizing solution was kept constant at 72 F. All samples were anodized for 60 minutes followed by a 10 minute seal in water at 185 F. and then allowed to air dry.

It is readily seen from Table I that the gold colored composite articles produced by anodizing the chromium containing aluminum alloys of this invention are superior in light fastness to the gold colored articles produced by coloring the anodic coatings of conventional aluminum alloys by prior art coloring methods.

The following Table 11 illustrates further alloys of this invention, together with statements as to color and brightness or lustre of the surface of the alloys after being rolled into sheet and anodized for 60 minutes in a 15 sulfuric acid solution with a current density of 12 amperes per square foot and wherein the temperature of the electrolyte was 72 F.

Table 11 Percent Percent Percent Percent Percent Percent Percent Percent Color Brightness or T1 Mg Mn Si Fe Cu Al 0. 40 0. 01 0. 07 0. 04 B511. Medium gold Bright. 0. 41 0. 03 0. 08 0.10 0. 02 B81. d D0. 0.36 0.03 0.07 0. 08 0.01 E31. 0 D0. 0.30 0. 03 0. 12 0. 18 0.03 B21. Light gold Slightly difiuse. 0. 34 0.03 0.12 0.17 0. 04 B81. do D0. 0.38 0. 0t 0. 00 0.10 Tr. Bal. Medium gold Do. 0. 38 0.03 0. 08 0.16 0, 02 Bel. do Do. 0. 40 0. 05 0. 014 0.003 Tr. Bal. Very bright. 0.39 0.10 0.012 0. 003 Tr Bal. D0. 0. 38 0.005 0. 003 Tr B211. DO.. 0. 39 0. 07 0. 005 0.009 1331. Do. 0. 38 0.09 0. 01 0. 02 Bal. D0. 0.31 0.03 0.06 0.09 0 01 B81. Bright. 0. 37 0. 04 0. 06 0. 09 0. 01 1351. Do. 0.40 0. 0-1 0 35 0. 08 0.12 B211. D0. 0. 45 0. 04 0 31 0.11 0.15 0. 04 1331. D0. 0. 38 0. 04 0. 06 0.10 0. 01 Ba]. Do. 0.39 0. 03 0 35 0. 08 0.12 0.01 E31. D0.

The following Table III illustrates further alloys of this invention, together with statements as to color and brightness or lustre of the surface of the alloys after being rolled into sheet and anodized in a 5% oxalic acid solution for time periods of 15, 30 and 45 minutes. The current density was 18 amperes per square foot and the colors. Too, the superior light fastness of the colored coatings makes possible the use of the colored composite articles, for example, automotive trim, building panels, etc., in an outdoor exposure Without and fading of the color.

It will be understood that various changes, omissions temperature of the electrolyte was 85 F. and additions may be made to this invention without de- T able 111 Per- Per- Per- Per- Per- Per- Anodizcent cent cent ent cent cent ing time, Color Brightness Cr Ti 1 Fe Cu Al minutes 0. 29 0. 03 0. 07 0. 10 T! Bel. 15 Light gold Bright.

0.29 0. 03 0. 07 0. 10 Tr Bal. 30 Medium gold Do.

0. 29 0. 03 0. 07 0. 1O Tr Bal. 45 Deep g0ld D0.

0. 38 0. 03 0. 07 0. l2 Tr Bal. 15 Light gold D0.

0. 38 0.03 0. 07 0. 12 Tr Bal 30 Deep gold Do.

0. 38 0.03 0. 07 0. 12 Tr Bal. 45 Very deep gold Do.

The following Table IV illustrates further alloys of 40 this invention together with statements of color and rightness when the alloys are in the form of extrusions which have been anodized in a 5% oxalic acid solution for thirty minutes using a current density of 18 amperes parting from the spirit and scope thereof as set forth in the appended claims.

All percentages in the claims are by Weight of the total alloy.

-What is claimed is:

per square foot and a solution temperature of 85 F. 1. An alluminum base alloy' consisting essentially of Table IV Per- Per- Per- Per- Per- Percent cent cent cont cent cent Color Brightness Or Tl Mg Si Fe Al 0.39 0.03 0.40 0.05 0.08 1321. Deep gold Slightly difiuse.

0. 29 0. 03 0. 41 0.05 0. 08 B21. Medium gold D0.

0.39 0.03 0.05 0.07 Bel. Deep g0ld Bright.

0. 38 0.03 0.05 0. 07 B211. do D0.

0. 29 0. 04 0.05 0. 08 Ba]. Medium gold- Do.

0. 40 0. 08 1.03 0. 01 0. 01 Bal. Deep gold Very bright.

0.34 0.09 0. 96 0. 01 0, 01 Bal. Medium gold- Do.

It will thus he been that by the present invention aluminum base alloys have been provided whereby upon anodizing a very pleasing colored composite article is produced without the necessity of subjecting the anodized surface to a separate coloring treatment and wherein the colors are reproducible.

The alloys of this invention are particularly suitable 'for manufacturing numerous articles from rolled sheet or extruded shapes, such as automotive trim, exterior architectural applications, furniture, household goods, etc.

'Also, articles drawn from sheet stock, such as bowls,

reflectors, etc., may also be made from these alloys.

The gold or bronze colored anodic oxide film which is produced on the alloys of this invention not only atfords abrasion and corrosion protection to the underlying aluminum alloy surface but also makes possible a wide choice of pleasing and decorative shades of gold or bronze normal amounts and wherein the total amount present.

of iron and silicon impurities is not in excess of 0.35%, the constituents being present in controlled amounts such that a bronze color is obtained upon electrolytic anodizing.

3. An aluminum base alloy consisting essentially of from about 0.2 to 0.5% chromium, from about 0.2 to 0.6% manganese, from about 0.02 to 0.10% titanium,

balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, the constituents being present in controlled amounts such that a bronze color is obtained upon electrolytic anodizing.

4. An aluminum base alloy consisting essentially of from about 0.2 to 0.5% chromium, from about 0.2 to 1.2% magnesium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, the constituents being present in controlled amounts such that a golden color is obtained upon electrolytic anodizing.

5. An aluminum base alloy consisting essentially of from about 0.2 to 0.5 chromium, from about 0.2 to 1.2% magnesium, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, the constituents being present in controlled amounts such that a golden color is obtained upon electrolytic anodizing.

6. An aluminum base alloy consisting essentially of from about 0.2 to 0.5% chromium, from about 0.2 to 1.2% magnesium, from about 0.2 to 0.6% manganese, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, the constituents being present in controlled amounts such that a bronze color is obtained upon electrolytic anodizing.

7. An aluminum base alloy consisting essentially of from about 0.2 to 0.4% chromium, from about 0.4 to 0.6% magnesium, from about 0.2 to 0.6% manganese, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, the constituents being present in controlled amounts such that a bronze color is obtained upon electrolytic anodizing.

8. An aluminum base alloy consisting essentially of 0.35 chromium, 0.04% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.20%, the constituents being present in controlled amounts such that a golden color is obtained upon electrolytic anodizing.

9. An aluminum base alloy consisting essentially of 0.35% chromium, 0.04% titanium, 0.5 magnesium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.20%, the constituents being present in controlled amounts such that a golden color is obtained upon electrolytic anodizing.

10. An aluminum base alloy consisting essentially of 0.4% chromium, 1.0% magnesium, 0.08% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.03%, the constituents being present in controlled amounts such that a golden color is obtained upon electrolytic anodizing.

11. A composite article comprising a base portion of an aluminum base alloy having a gold colored anodic oxide film adhering thereto, said aluminum base alloy consisting essentially of from about 0.2 to 0.5% chromium, from 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%.

12. A composite article comprising a base portion of an aluminum base alloy having a bronze colored anodic oxide film adhering thereto, said alloy consisting essentially of from about 0.2 to 0.5% chromium, from about 0.2 to 0.6% manganese, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 13. A composite article comprising a base portion of an aluminum base alloy having a bronze colored anodic oxide film adhering thereto, said alloy consisting essentially of from about 0.2 to 0.5% chromium, up to about 0.6% manganese, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%.

14. A composite article comprising a base portion of an aluminum base alloy having a gold colored anodic oxide film adhering thereto, said aluminum base alloy consisting essentially of from about 0.2 to 0.5% chromium, from about 0.2 to 1.2% magnesium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%.

15. A composite article comprising a base portion of an aluminum base alloy having a gold colored anodic oxide film adhering thereto, said aluminum base alloy consisting essentially of from about 0.2 to 0.4% chromium, from about 0.4 to 0.6% magnesium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%.

16. A composite article comprising a base portion of an aluminum base alloy having a gold colored anodic oxide film adhering thereto, said aluminum base alloy consisting essentially of from about 0.2 to 0.5% chromium, up to about 1.2% magnesium, 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%.

17. A composite article comprising a base portion of an aluminum base alloy having a gold colored anodic oxide film adhering thereto, said aluminum base alloy consisting essentially of from about 0.2 to 0.5% chromium, up to about 1.2% magnesium, up to about 0.6% manganese, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%.

18. A composite article comprising a wrought base portion of an aluminum base alloy having a gold colored anodic oxide film adhering thereto, said aluminum base alloy consisting essentially of 0.35% chromium, 0.04% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impuriites is not. in excess of 0.2%.

19. A composite article comprising a wrought base portion of an aluminum base alloy having a gold colored anodic oxide film adhering thereto, said aluminum base alloy consisting essentially of 0.35% chromium, 0.04% titanium, 0.5% magnesium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.2%.

20. A composite article comprising a wrought base portion of an aluminum base alloy having a gold colored anodic oxide film adhering thereto, said aluminum base alloy consisting essentially of 0.4% chromium, 1.0% magnesium, 0.08% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.03%.

21. A composite article comprising a layer of a high strength aluminum base alloy, clad on at least one surface With a layer of a second aluminum base alloy of lower strength and a layer of a gold colored anodic oxide film adhering to the surfaw of said second aluminum base alloy layer, said second aluminum base alloy layer consisting essentially of from about 0.2 to 0.5%

a chromium, from about 0.02 to 0.10% titanium, balance strength aluminum base alloy, clad on at least one surface with a layer of a second aluminum base alloy of lower strength and a layer of bronze colored anodic oxide film adhering to said second aluminum base alloy layer, said second aluminum base alloy layer consi ing essentially of from about 0.2 to 0.5% chromium, from about 0.02 to 0.10% titanium, up to about 0.6% manganese, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%.

23. A composite article comprising a layer of high strength aluminum base alloy, clad on at least one surface with a layer of a second aluminum base alloy of lower strength and a layer of gold colored anodic oxide film adhering to said second aluminum base alloy layer, said second aluminum base alloy layer consisting essentially from about 0.2 to 0.5% chromium, up to about 1.2% magnesium, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%.

24. A composite article comprising a layer of wrought high strength aluminum base alloy, clad on at least one surface with a layer of a second wrought aluminum base alloy of lower strength and a layer of gold colored anodic oxide film adhering to said second aluminum base alloy layer, said second aluminum base alloy layer consisting essentially of 0.35% chromium, 0.04% 'tanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.2%.

25. A process for producing gold colored aluminum base alloy articles characterized by superior light fastness and desirable appearance comprising the steps of providing an aluminum base alloy article consisting essentially of from about 0.2 to 0.5% chromium, balance aluminum and impurities in normal amounts and Wherein the total amount present of iron and silicon impurities is not in excess of 0.35 exposing said article as an anode to an electric current in a 2 to oxalic acid electrolyte maintained at a temperature of from about 75 to 100 F. for a period of from about to 90 minutes while maintaining the electric current at an anode current density of from about 10 to 30 amperes per square foot.

26. A process for producing gold colored aluminum base articles characterized by superior light fastness and desirable appearance comprising the steps of providing an aluminurn base alloy article consisting essentially of from about 0.2 to 0.5% chromium, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, exposing said article as an anode to electric current in a 2 to 10% oxalic acid electrolyte maintained at a temperature of from about 75 to 100 F. for a period or" from about 15 to 90 minutes while maintaining the electric current at an anode current density of from about 10 to 30 amperes per square foot.

27. A process for producing gold colored aluminum base articles characterized by superior light fastness and desirable appearance comprising the steps of providing an aluminum base alloy article consisting essentially of from about 0.2 to 0.5% chromium, up to about 1. 2% magnesium, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, exposing said article as an anode to electric current in a 2 to 10% oxalic acid electrolyte maintained at a temperature of from about 75 to 100 F. for a period of from about 15 to 90 nunuteswhile maintaining the electric current at an anode current den:

sity of from about 10 .to 30 amperes per square foot.

' 28. A process for producing gold colored aluminum base alloy articles characterized by superior light fastness and desirable appearance which comprises the steps of providing an aluminum base article consisting essentially of from about 0.2 to 0.5% chromium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, exposing said article as an anode to electric current in a 10 to 20% sulfuric acid electrolyte maintained at a temperature of from about 60 to F. for a period of from about 30 to minutes while maintaining the electric current at an anode current density of 5 to 2'0 amperes per square foot.

29. A process for producing gold colored aluminum base alloy articles characterized by superior light fastness and desirable appearance which comprises the steps of providing an aluminum base article consisting essentially of from about 0.2 to 0.5% chromium, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35 exposing said artiole as an anode to electric current in a 10 to 20% sulfuric acid electrolyte maintained at a temperature of from about 60 to 85 F. for a period of from 30 to 90 minutes While maintaining the electric current at an anode current density of from about 5 to 20 amperes per square foot.

30. A process for producing bronze colored aluminum base alloy articles characterized by superior light fastness and desirable appearance which comprises the steps of providing an aluminum base article consisting essentially out from about 0.2 to 0.5 chromium, up toabout 0.6% manganese, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, exposing said article as an anode to electric current in a 1 0 to 20% sulfuric acid electrolyte maintained at a temperature of from about 60 to 85 F. for a period of from about 30 to 90 minutes while maintaining the electric current at an anode current density of from about 5 to 20 amperes per square foot.

31. A process for producing gold colored aluminum base alloy articles characterized by superior light tastness and desirable appearance which comprises the steps of providing an aluminum base article consisting essentially of from about 0.2 to 0 .5% chromium, up to about 1.2% magnesium, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35 exposing said anticle as an anode to electric current in a 10 to 20% sulfuric acid electrolyte maintained at a temperature of from about 60 to 85 F. for a period of from about 30 to 90 minutes while maintaining the electric current at an anode current density of from about 5 to 20 amperes per square toot.

32. A process for producing gold colored aluminum base alloy articles characterized by superior light fas-t-ness and desirable appearance comprising the steps of providing an aluminum base alloy article consisting essentially of from about 0.2 to 0.5 chromium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35 exposing said article as an anode to an electric current in an electrolyte comprising 2 to 10% oxalic acid and 5 to 15% sulfuric acid maintained at a temperature from about 75 to F. for a period of from about 15 to 90 minutes while maintaining the electric current at an anode cur-rent density of from about 10 to 30 amperes per square foot.

33. A process for producing gold colored aluminum base articles characterized by superior light fastness and desirable apparance comprising the steps of providing an aluminum base alloy article consisting essentially of from about 0.2 to 0.5% chromium, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35 exposing said article as an anode to an electric current in an electrolyte comprising 2 to oxalic acid and 5 to sulfuric acid maintained at a temperature from about 75 to 100 F. for a period of from about 15 to 90 minutes while maintaining the electric current at anode density of from about 10 to amperes per square foot.

34. A process for producing gold colored aluminum base articles characterized by superior light fastness and desirable appearance comprising the steps of providing an aluminum base alloy article consisting essentially of from about 0.2 to 0.5% chromium, up to about 1.2% magnesium, from about 0.02 to 0.10% titanium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, exposing said article as an anode to an electric current in an electrolyte comprising 2 to 10% oxalic acid and 5 to 15% sulfuric acid maintained at a temperature from about to 100 F. for a period of from about 15 to minutes While maintaining the electric current at an anode current density of from about 10 to 30 amperes per square foot.

35. An aluminum base alloy consisting essentially of from about 0.2 to 0.4% chromium, from about 0.4 to 0.6% magnesium, balance aluminum and impurities in normal amounts and wherein the total amount present of iron and silicon impurities is not in excess of 0.35%, the

constituents being present in controlled amounts such that a golden color is obtained upon electrolytic anodizing.

References Cited in the file of this patent UNITED STATES PATENTS 1,910,861 Keller et a1 May 23, 1933 1,975,105 Keller Oct. 2, 1934 2,084,327 Edwards June 22, 1937 2,208,186 Igarashi July 16, 1940 2,212,266 Coles Aug. 20, 1940 2,312,039 Hoglund Feb. 23, 1943 2,584,400 Sonino Feb. 5, 1952 2,614,690 Stoneman Oct. 21, 1952 2,685,563 Gauthier Aug. 3, 1954 FOREIGN PATENTS 460,476 Canada Oct. 18, 1949 159,008 Great Britain Nov. 18, 1939 OTHER REFERENCES Harrington: Transaction ASM, vol. 41, 1949, pp. 443- 444, published by American Society for Metals, Cleveland, Ohio.

Coatings for Metals, Burns and Bradley, published by Reinhold Publishing Company, 430 Park Avenue, New York, published 1955, pages 556-564.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,107, 159 October 15 1963 Maurice C9 Fetzer et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5 line 32, for "Slufuric" read Sulfuric column 6 line l7 for "0.5% zinc" read 0.05% zinc column 8, line 23 for "and" read any line 45, for "alluminum" read aluminum column 10 line 47 for "impuriites" read impurities Signed and sealed this 9th day of June 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

21. A COMPOSITE ARTICLE COMPRISING A LAYER OF A HIGH STRENGTH ALUMINUM BASE ALLOY, CLAD ON AT LEAST ONE SURFACE WITH A LAYER OF A SECOND ALUMINUM BASE ALLOY OF LOWER STRENGTH AND A LAYER OF A GOLD COLORED ANODIC OXIDE FILM ADHERING TO THE SURFACE OF SAID SECOND ALUMINUM BASE ALLOY LAYER, SAID SECOND ALUMINUM BASE ALLOY LAYER CONSISTING ESSENTIALLY OF FROM ABOUT 0.2 TO 0.5% 